A drop-in replacement ThreadLocal implementation that does not leak when thread-local values reference the ThreadLocal object. The code is optimised to cope with frequently changing values.

In comparison to plain ThreadLocal, this implementation:

from the point of view of a single thread, each thread-local {code #get} requires access to four objects instead of two
is fractionally slower in terms of CPU cycles for {code #get}
uses around twice the memory for each thead-local value
uses around four times the memory for each ThreadLocal
may release thread-local values for garbage collection more promptly

Nested and Inner Type Summary

Modifier and Type	Class and Description
private static class	VicariousThreadLocal.Holder Holds strong reference to a thread-local value.

Field Summary

Modifier and Type	Field and Description
private final ThreadLocal<WeakReference<VicariousThreadLocal.Holder>>	local Actual ThreadLocal implementation object.
private final ReferenceQueue<Object>	queue Queue of Holders belonging to exited threads.
private volatile VicariousThreadLocal.Holder	strongRefs Maintains a strong reference to value for each thread, so long as the Thread has not been collected.
private static final AtomicReferenceFieldUpdater<VicariousThreadLocal<T>, VicariousThreadLocal.Holder>	strongRefsUpdater Compare-and-set of `strongRefs`.
private static final Object	UNINITIALISED Object representing an uninitialised value.
private static final ThreadLocal<WeakReference<Thread>>	weakThread Maps a unique WeakReference onto each Thread.

Constructor Summary

Access	Constructor and Description
public	VicariousThreadLocal() Creates a new `VicariousThreadLocal`.

Method Summary

Modifier and Type	Method and Description
private VicariousThreadLocal.Holder	createHolder() Creates a new holder object, and registers it appropriately.
pack-priv static WeakReference<Thread>	currentThreadRef() Returns a unique object representing the current thread.
public T	get() Overrides java.lang.ThreadLocal.get. Returns the value in the current thread's copy of this thread-local variable.
public void	poll() Check if any strong references need should be removed due to thread exit.
public void	remove() Overrides java.lang.ThreadLocal.remove. Removes the current thread's value for this thread-local variable.
public void	set(T the value to be stored in the current thread's copy of this thread-local. value) Overrides java.lang.ThreadLocal.set. Sets the current thread's copy of this thread-local variable to the specified value.

Inherited from java.lang.ThreadLocal:: initialValue withInitial

Field Detail

local	back to summary
private final ThreadLocal<WeakReference<VicariousThreadLocal.Holder>> local Actual ThreadLocal implementation object.

queue	back to summary
private final ReferenceQueue<Object> queue Queue of Holders belonging to exited threads.

strongRefs	back to summary
private volatile VicariousThreadLocal.Holder strongRefs Maintains a strong reference to value for each thread, so long as the Thread has not been collected. Note, alive Threads strongly references the WeakReference<Thread> through weakThread.

strongRefsUpdater	back to summary
private static final AtomicReferenceFieldUpdater<VicariousThreadLocal<T>, VicariousThreadLocal.Holder> strongRefsUpdater Compare-and-set of `strongRefs`.

UNINITIALISED	back to summary
private static final Object UNINITIALISED Object representing an uninitialised value.

weakThread	back to summary
private static final ThreadLocal<WeakReference<Thread>> weakThread Maps a unique WeakReference onto each Thread.

Constructor Detail

VicariousThreadLocal	back to summary
public VicariousThreadLocal() Creates a new `VicariousThreadLocal`.

Method Detail

createHolder	back to summary
private VicariousThreadLocal.Holder createHolder() Creates a new holder object, and registers it appropriately. Also polls for thread-exits.

currentThreadRef	back to summary
pack-priv static WeakReference<Thread> currentThreadRef() Returns a unique object representing the current thread. Although we use a weak-reference to the thread, we could use practically anything that does not reference our class-loader.

get back to summary

get	back to summary
public T get() Overrides java.lang.ThreadLocal.get. Doc from java.lang.ThreadLocal.get. Returns the value in the current thread's copy of this thread-local variable. If the variable has no value for the current thread, it is first initialized to the value returned by an invocation of the `initialValue` method. Returns:T the current thread's value of this thread-local Annotations @SuppressWarnings:unchecked @Override

public T get()

Overrides java.lang.ThreadLocal.get.

Doc from java.lang.ThreadLocal.get.

Returns the value in the current thread's copy of this thread-local variable. If the variable has no value for the current thread, it is first initialized to the value returned by an invocation of the initialValue method.

Returns:T

the current thread's value of this thread-local

Annotations

@SuppressWarnings:unchecked
@Override

poll	back to summary
public void poll() Check if any strong references need should be removed due to thread exit.

remove back to summary

remove	back to summary
public void remove() Overrides java.lang.ThreadLocal.remove. Doc from java.lang.ThreadLocal.remove. Removes the current thread's value for this thread-local variable. If this thread-local variable is subsequently read by the current thread, its value will be reinitialized by invoking its `initialValue` method, unless its value is set by the current thread in the interim. This may result in multiple invocations of the `initialValue` method in the current thread. Annotations @Override

public void remove()

Overrides java.lang.ThreadLocal.remove.

Doc from java.lang.ThreadLocal.remove.

Removes the current thread's value for this thread-local variable. If this thread-local variable is subsequently read by the current thread, its value will be reinitialized by invoking its initialValue method, unless its value is set by the current thread in the interim. This may result in multiple invocations of the initialValue method in the current thread.

Annotations

@Override

set back to summary

set	back to summary
public void set(T value) Overrides java.lang.ThreadLocal.set. Doc from java.lang.ThreadLocal.set. Sets the current thread's copy of this thread-local variable to the specified value. Most subclasses will have no need to override this method, relying solely on the `initialValue` method to set the values of thread-locals. Parameters value:T the value to be stored in the current thread's copy of this thread-local. Annotations @Override

public void set(T value)

Overrides java.lang.ThreadLocal.set.

Doc from java.lang.ThreadLocal.set.

Sets the current thread's copy of this thread-local variable to the specified value. Most subclasses will have no need to override this method, relying solely on the initialValue method to set the values of thread-locals.

Parameters

value:T: the value to be stored in the current thread's copy of this thread-local.

Annotations

@Override

net.sf.ehcache.util.lang back to summary

private Class VicariousThreadLocal.Holder

Class Inheritance

extends WeakReference<Object>

java.lang.Object
java.lang.ref.Reference
java.lang.ref.WeakReference
net.sf.ehcache.util.lang.VicariousThreadLocal.Holder

Holds strong reference to a thread-local value. The WeakReference is to a thread-local representing the current thread.

Field Summary

Modifier and Type	Field and Description
pack-priv VicariousThreadLocal.Holder	next Hides java.lang.ref.Reference.next. Next holder in chain for this thread-local.
pack-priv Object	value Current thread-local value.

Constructor Summary

Access	Constructor and Description
pack-priv	Holder(ReferenceQueue<Object> queue) Construct a new holder for the current thread.

Field Detail

next	back to summary
pack-priv VicariousThreadLocal.Holder next Hides java.lang.ref.Reference.next. Next holder in chain for this thread-local.

back to summary

pack-priv VicariousThreadLocal.Holder next

Hides java.lang.ref.Reference.next.

Next holder in chain for this thread-local.

value	back to summary
pack-priv Object value Current thread-local value. `UNINITIALISED` represents an uninitialised value.

Constructor Detail

Holder	back to summary
pack-priv Holder(ReferenceQueue<Object> queue) Construct a new holder for the current thread.

public Class VicariousThreadLocal<T>

Nested and Inner Type Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail

private Class VicariousThreadLocal.Holder

Field Summary

Constructor Summary

Field Detail

Constructor Detail